1. Field of Invention
The present invention relates to an illumination apparatus, and more particularly to an asymmetrical illumination apparatus.
2. Related Art
The main purpose of street lighting is to enhance and guarantee night traffic safety. For driving, street lighting enables drivers to see the forward visual field more clearly, so as to take safety measures timely within an appropriate distance. This safety distance is closely related to the street lighting, the speed of the vehicle, the road condition, the performance of the vehicle, and the reaction capacity of the driver. However, seen from the illumination design point, the street lighting and the speed of the vehicle are the most critical.
Glare, a phenomenon that the light within the visual field of a human eye causes discomfort or blurred vision, is one of the factors that affect the quality of the street lighting. The conventional illumination apparatus of a street lamp has a light intensity peak value distributed at an angle of 60° from a vertical direction, so that the light may be irradiated straightforward into the human eye to form a direct glare. As a result, the driver may easily feel an eye fatigue and will be in a dangerous situation. Moreover, the conventional light source usually forms symmetrically shapes of circles or ellipses on the road surface. If a large range of the road surface is to be lighted, plenty of lights will be projected on places outside the road surface to cause light waste and pollution. Further, if the irradiated light form is to be adjusted by a reflector, a deeper reflector is required to get a satisfactory result, but the weight and size of the lamp will be huge.
Referring to US Patent Publication No. 3,766,375, prisms disposed on a reflector and a lampshade are used to adjust the light form to match a conventional light bulb, so as to produce an asymmetrical light field distribution.
Referring to US Patent Publication No. 3,775,605, No. 4,041,306, No. 4,096,555, No. 4,358,816, and No. 4,651,260, various reflective lampshades in different structures are used for reflecting to match a conventional light bulb, so as to produce an asymmetrical light field distribution.